SAN FRANCISCO (CBS SF) — The San Francisco Municipal Transportation Agency employees who called in sick Tuesday will have to provide verification from their health care provider in order to be eligible to receive paid sick leave, according to an email memo sent to Muni employees Tuesday morning.

Agency spokesman Paul Rose said if Muni drivers want to use one of the 13 sick days a year for Tuesday, they’re going to need a doctor’s note–a decision applauded by the San Francisco Chamber of Commerce.

“It’s time to get real,” said San Francisco Chamber of Commerce President Bob Linscheid. “Muni workers are the second highest paid transit operators in the country. Muni worker’s ‘sickout’ is nothing short of a strike – a clear violation of the City Charter.”

Mayor Edwin Lee responded in a statement Tuesday saying he joins in Muni riders’ frustrations over the disrupted service.

“The public should not be punished any longer,” Lee said. “I would like to thank the drivers who did not participate in this illegal action and did their best to keep our city moving.”

The president of the union representing MTA employees said his office had nothing to do with the worker “sickout” that left half of Muni’s vehicle fleet out of service Tuesday morning.

“The union played no role in what’s happening on the streets right now, we did not sanction that,” said Eric Williams, president of Transport Workers Union Local 250-A.

MTA added an additional 100 vehicles to the system but notified commuters to expect major delays citywide.

All express and limited buses will be stopping at every stop unless the bus reaches full capacity, and cable cars will be supplemented with limited shuttle buses, Muni officials said.

BART will also honor all Muni fares between the Daly City and Embarcadero stations.

MTA is advising customers to find alternative means of transportation and visit SFMTA’s website to find out which rail lines and bus routes will not operate Tuesday. For real-time updates, customers can also follow Muni on Twitter.

San Francisco Supervisor Scott Wiener said he plans to introduce a resolution at Tuesday’s Board of Supervisors meeting urging San Francisco Municipal Transportation Agency drivers to end their “sickout” and return to work.